Gesture Recognition Biofeedback

ABSTRACT

A gesture recognition biofeedback device is provided for improving fine motor function in persons with brain injury. The system detects a physical characteristic of the patient and provides feedback based on the detected characteristic. For instance, the system may detect surface muscle pressures of the forearm to provide real-time visual biofeedback to the patient based on a comparison of the detected muscle pressure and predefined values indicative of appropriate motor function.

PRIORITY STATEMENT

This application claims priority to U.S. Provisional Patent ApplicationNos. 61/447,466 filed on Feb. 28, 2011 and 61/447,980 filed on Mar. 1,2011. The entire disclosure of each of the foregoing applications isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to the field of providing therapy forindividuals suffering a brain injury. In particular, the presentinvention is directed to a system for providing biofeedback to a patientduring a therapeutic activity to improve the effectiveness of thetherapy.

BACKGROUND

Grasping is fundamental to activities of daily living (ADL) and isusually impaired following stroke and traumatic brain injury. In theabsence of grasping, the impaired arm tends to be neglected, retardingits recovery; accordingly, grasp training is a high priority forrehabilitation of the upper limb.

Repetitive training tasks are often difficult for brain injuredindividuals, due not only to their motor deficits, but also to theirtactile and proprioceptive deficits. Although there are reports in theliterature of inconclusive evidence, many studies many studies havedocumented the efficacy of EMG biofeedback. For example, a group ofhemiplegic patients who were given occupational therapy plusEMG-biofeedback improved their upper limb function relative to a controlgroup receiving only occupational therapy]. Biofeedback from the EMGs ofthe extensor carpi radialis and extensor digitorum communis improved thewrist and finger extension of stroke subjects. EMG biofeedback has evenbeen proposed as a therapy for remotely supervising home users. Themethod, however, remains a challenge, as EMG requires expertise and isdifficult for self-application and interpretation. A more fundamentalproblem of using EMG for biofeedback is that electrical activities ofmuscle vary considerably from one repetition to the next, even when theunderlying movement is kinematically consistent.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schema of a Gesture Recognition Biofeedback recordingsystem.

FIG. 2. is a graphical representation of training results for 12impaired subjects, grouped equally according to training order, eitherWF-NF or NF-WF. Note that HPT scores (as percent of baseline, mean±S.E.)were better for the WF condition in both groups.

FIG. 3. Is a graphical representation of the changes in HPT scores (aspercent of baseline, mean±S.E.). The left comparison represents resultsfrom all impaired subjects; the center comparison represents resultsfrom a more impaired subset of subjects; and the right comparisonrepresent results from the control subjects.

DETAILED DESCRIPTION

Referring now to the Figures In general and to FIG. 1 specifically, asystem for providing gesture recognition biofeedback (GRB) for improvingfine motor function in individuals who have a brain injury is designatedgenerally 10. The system uses visual feedback to relay the accuracy ofspecific gestures and uses a simpler interface than systems relying uponspecific muscular activation amplitudes.

The system 10 includes a sensing device 20 for sensing muscularoperation of a subject. The sensing device 20 provides electricalsignals to a processor 30, which processes the signals received from thesensing device. Based on the signals received from the sensing device,the processor provides visual feedback on a display, such as a videodisplay 30.

The sensing device 20 may be designed to be readily attachable to apatient. For instance, in the present instance, the sensing deviceincludes a cuff 22 that can be placed around the forearm of the patient.The cuff 22 may be adjustable, such as by an elastic band or a fastener,such as a hook and loop fastener. The sensing device 20 includes one ormore sensors or detectors 24 for detecting a physical characteristic. Inthe present instance, the sensing device includes seven sensors 24 fordetecting muscle contraction. Specifically, the sensors 24 are forcesensors for detecting force applied against the sensor when the sensoris against or adjacent the skin of the patient.

The processor 30 may be any of a variety of processors, such as themicroprocessor of a personal computer. The processor may be electricallyconnected with the sensing device by a wired connection, such as acable. Alternatively, the sensing device 20 may include a wirelesstransmitter for wirelessly transmitting the signals from the sensors.The processor 30 may be connected with a wireless receiver for receivingwireless signals from the sensing device 20.

The processor 30 processes the signals from the sensing device todetermine whether the signals indicate a desired type of movement. Thedesired type of movement may by a specific movement from the patient ora specific amount of movement or both. In the present instance, theprocessor monitors the signals from the sensing device 20 to detectwhether the signals indicate an appropriate grasping motion by thepatient. Specifically, the processor 30 compares the signals receivedfrom the sensing device during a therapy session and compares thesignals against predetermined values. Based on the comparison, theprocessor 30 determines whether the signal indicates the desiredgrasping motion.

The processor 30 provides signals to an output mechanism for providingfeedback to the patient. The output mechanism may be any of a variety ofdevices providing visual, auditory or tactile feedback to the patient.For instance, the output mechanism can be a speaker to provide an audialcue to the patient that the patient can hear to determine whether or notthe patient made the desired movement, such as a grasping motionsufficient to grasp an item. Similarly, the output mechanism may providetactile feedback, such as a motor for providing a vibration. In thepresent instance, the output mechanism is a display, such as a videoscreen. The display provides a graphical image to signal the patient ifthe patient made the desired movement.

The system may also include an output mechanism for prompting thepatient in addition to the output mechanism for the biofeedbackdiscussed above. As with the biofeedback element discussed above, theoutput mechanism can be used to provide a visual, audial and/or tactilesignal to the user. For instance, the system 10 may include an audiodevice for providing audial cues to the patient., which may be used toprompt the patient to perform a particular task. Alternatively, thebiofeedback mechanism can also be used to provide to prompt the patient.For instance, the display 40 may include a signal to perform aparticular task along with an image providing biofeedback about thepatient's performance of the task.

In the present instance, the sensing element 20 uses Surface MusclePressure (SMP) to record muscle activation during fine motor tasks. SMPregisters voluntary effort during grasping with the sensorized cuff wornon the forearm. Gesture recognition feedback operates by displaying thedifference between SMP sensor outputs and a pre-recorded gesturetemplate defined as directed by a clinician providing the user withguidance in repetitive task performance that can be remotely monitored.

EXAMPLE Participants

The system 10 was used with an experimental group comprising both stroke(n=4) and TBI (n=8) subjects, 8 male and 4 female. Ten of the subjectswere right-hand dominant. Their mean age was 39.8 years, with a range of21 to 69 years. All had mild to moderate spasticity, as assessed by anOccupational Therapist, and could complete the 9-Hole Peg Test (HPT). Inaddition to the experimental group, seven healthy subjects participatedas a cohort of control subjects, approximately age-matched to theexperimental group, with a mean age of 46.4 years ranging from 25 to 67years. None reported any neurological or biomechanical impairment ineither upper extremity.

Biofeedback

The sensing device 20 monitored surface muscle pressure (SMP). The SMPwas recorded with a sensorized therapeutic cuff placed comfortablyaround the forearm. The sensing device included seven 0.5″ diameterforce sensing resistors made by Interlink Electronics. The sensors 24were moveable within the cuff 22 so that the sensors could be evenlyspaced around each subject's forearm. While the sensors were distributeduniformly, they were not targeted to specific locations on the arm.Signals from the sensing device 20 were acquired at a sampling rate of25 Hz. The cuff was applied around the forearm with a comfortable staticpressure, providing a positive baseline that allowed detection of localpressure changes in the limb.

Biofeedback was generated as a comparison between real-time SMP valuesand those previously recorded as a template for desirable activity. Toset the template, subjects were instructed to continue resting while the“relax” state was captured. Subjects were then instructed to “pinch”,producing a thumb-index opposition, with attention to the posture of thehand. SMP values from the final 200 ms of capture were averaged togenerate a template value for each sensor.

For training, subjects were given auditory cues to pinch and relax,alternately presented every 4 seconds. Biofeedback was generated as ascalar value, which was derived from the multi-dimensional informationfrom all seven SMP sensors. The pinch template was defined as a staticpoint in sensor space whose location was defined during templatesetting. The real-time SMP values defined a point in the sensor spacerepresentative of forearm muscle activity.

During set-up, a clinician can monitor the movement of the patient asthe patient performs a desired task, such as pinching. While guidingand/or monitoring the patient during the task, the sensing device canmonitor the patient's movement by providing SMP values to a processor.Since the clinician is observing the patient, the clinician can ensurethat the patient's movement was acceptable. The processor can thenanalyze the SMP values to determine a template of predetermined SMPvalues for each of the sensors corresponding to an acceptable movementby the particular patient.

In the present instance, to resolve the real-time and template SMPvalues into information about performance, their locations were comparedusing the Euclidean distance, a simple spatial metric that decreased asthe real-time SMP approached the template in sensor space, calculated as

GRB=10−,−,1=1−7− , , , Target−i.−,SMP−i . . . 2  Equation 1

A display provided feedback by displaying an image of a tank whosefullness was determined by the GRB feedback value based on signals fromthe sensing device. The image provided increased visual feedback asthumb-index opposition more closely met the clinician-directed template.

Protocol

During training, subjects were instructed to pinch as in templatesetting. In the With Feedback (WF) condition, visual feedback was givenas described above. In the No Feedback (NF) condition, the subject wasinstructed to either pinch or rest according to the auditory timingcues, but no visual feedback was given. Sessions included approximately30 repetitions per condition, with two rest periods provided asnecessary.

Participants were pseudo-randomly assigned to two groups, whichdetermined the order that feedback conditions were used in training. Onegroup (WF-NF) had biofeedback in the first training session and nofeedback during the second session. The NF-WF group was trained in theopposite order. The same grouping scheme was used for the controlsubjects.

Fine motor function was assessed by the HPT, which was administeredusing standard pegs and peg board. Subjects were instructed to fill theboard peg-by-peg, then to remove pegs one at a time. They wereinstructed to complete this test as quickly as possible and using onlythe affected hand. The HPT was performed three times during the study:first as a pre-training baseline, then after each of the two trainingconditions.

Analysis

Results from the HPT were compared within subjects as the differencebetween the time to completion of a test and that of the precedinginstance, normalized within subjects by dividing each difference by thebaseline time. To measure their independence from training order, HPTtimes were compared between the two training order groups. This analysiswas performed both for WF training and for NF training, using thenon-parametric Mann-Whitney test. Low significance from this analysiswould indicate that the training order was irrelevant and the two groupscould be combined.

HPT times following both NF and WF training were compared using theWilcoxon signed-rank test, as data were collected in two conditions foreach subject. In all cases, the null hypothesis of these tests was theexpectation that the two experimental conditions yielded identical timeson the HPT.

The inclusion criteria were additionally narrowed in further post-hocprocessing. Separately analyzing a subset of participants whose baselineHPT exceeded an arbitrary minimum allowed inferences about the efficacyof the device for users with more severe impairment. The arbitrary limitused herein was 50 seconds.

Results

For the impaired groups, the dependence of training order was analyzed,and no significant effect was found (p>0.7), as seen in FIG. 2. Based onthis result, the two groups were combined, and subsequent analyses wereconducted independently of training order. After one session of trainingby all impaired subjects with feedback (WF), the average decrease in HPTtime to completion was 16.1%±6.98%. In contrast, training with nofeedback (NF) slightly increased the HPT time by 2.07%±3.61% (FIG. 1).

A subset of the impaired subjects was established, using the criterionof a minimum of 50 seconds to complete the baseline HPT. This resultedin a cohort of seven subjects, treated as a single cohort regardless oftraining order. Results from this cohort of more severely impairedsubjects were compared to the results from the entire impaired group(FIG. 3). GRB training yielded an improvement of 27.3%±9.93%. In theabsence of GRB training, there was a 2.07%±3.61% decline in performance.The difference between the two was statistically significant (p<0.05).

GRB training negligibly affect HPT scores of the control subjects, asshown in FIG. 2. The minimal training effect was independent of trainingorders, and all controls were therefore combined into one cohort. Acrossall controls, the average HPT times after the WF and NF sessionsdecreased slightly by 1.31%±2.47%, and 0.74%±1.8%, respectively.

Discussion

Validity

Analyzing the efficacy of training with GRB is complicated by the rangeof impairments that result from brain injuries. Fine motor function wasassessed using an independent rater, the HPT, a commonly used outcomefor stroke rehabilitation. Since non-uniformity within the cohort ofbrain injured subjects was unavoidably present, statistical analyseswere non-parametric, and not based on the assumption of normaldistributions. The Mann Whitney and Wilcoxon signed rank tests weretherefore used to test significance.

Approximately 30 repetitions of the thumb-index opposition wereperformed in each training condition, split evenly into three sets byresting periods of approximately one minute. This number of repetitionswas sufficient to facilitate the improvement of fine motor functionduring training with biofeedback. However, without feedback, thirtyrepetitions were not likely to improve performance, even in the mostimpaired subjects.

It is possible that additional training time might have facilitated someimprovement in the NF condition. The total number of sixty repetitionsseemed to be the best compromise possible between avoiding fatigue andmaximizing training time. While some studies have used more repetitionsduring training, as many as two hundred, some have used only thirty tosixty repetitions.

The impaired group included 8 subjects with traumatic and 4 subjectswith ischemic brain injuries. Since no difference in trend was notedbetween the two injury types, we combined both types into a single groupusing a previously validated approach.

Experimental Design

Analyzing the efficacy of therapies for brain injuries due to trauma orstroke is complicated by the range of associated impairments. Here, finemotor function was assessed using an independent rater, the HPT, acommonly used outcome for stroke rehabilitation. The impaired groupincluded eight subjects with traumatic and four subjects with ischemicbrain injuries. Since no difference in trend was noted between the twoinjury types, we combined both types into a single group, similarly to aprevious approach, and used nonparametric statistical analysis, notbased on the assumption of normal distributions. In this way, subjects'changes in HPT time after WF training were compared to their own control(NF) condition.

Approximately 30 repetitions of the thumb-index opposition wereperformed in each training condition, split evenly into three sets byresting periods of approximately one minute. This number of repetitionswas sufficient to facilitate the improvement of fine motor functionduring training with biofeedback. However, without feedback, thirtyrepetitions were not likely to improve performance even in the mostimpaired subjects.

It is possible that additional training time might have facilitated someimprovement in the NF condition. The total number of 60 repetitionsseemed to be the best compromise possible between avoiding fatigue andmaximizing training time. While some studies have used more repetitionsduring training, as many as two hundred, some have used only 30-60repetitions.

Although the effects of stroke and TBI are thought to be generallydissimilar, the non-parametric, paired Wilcoxon signed-rank analysisused here treats improvements within subject.

The thumb-index opposition was selected as a representative task, as aprehensile movement critical to ADL and a common task in studies ofmotor control. The NF condition is representative of a typicalrehabilitation protocol, in which a subject repetitively performs a taskwithout a therapeutic device. It is similar to the control condition ina number of studies comparing new rehabilitative methods to standardtraining. Using both NF and WF training for each subject in a cross-overexperimental design allowed the use of a repeated-measures statisticalanalysis. The randomization of training orders accounted for thepossibly confounding effects of fatigue or other changes during anexperimental session. The close parallel between training effects forthe WF-NF group and the NF-WF group can be seen in FIG. 2, indicatingthe lack of effect of training order. For this reason, the possibilityof a confounding effect from fatigue, cognition, or other artifactualinfluences as detailed above can be dismissed as negligible.

Among the impaired subjects, there was a diversity of impairment level,as indicated by a wide range of baseline HPT time, from 28 to 263 s.Selecting a threshold of 52 s as a separation criterion resulted in asubset of seven more impaired subjects. As can be seen in FIG. 3, themore impaired group improved by 27.3% (S.D. 9.93%) with GRB which wassignificantly more efficacious than NF training.

Clinical Implications

The efficacy of acute training with GRB was tested in a pinching taskwith impaired subjects. Results from HPT testing showed that subjectsdecreased their time to completion of the HPT to a greater extent aftertraining with the biofeedback than after the no-feedback condition. GRBprovides real-time visual feedback during repetitive grasping tasks thatyields acute improvement in a single session of training. Since SMP doesnot require the precise placement of sensors on specific muscles, GRB iseasily donned and simple to interpret. GRB therefore offers the user asimple means for retraining fine motor function of the hand without thesupervision of a clinician. These results suggest that GRB has practicaladvantages over traditional biofeedback and can improve motor function,related to ADL in brain-injured individuals.

REFERENCES

The following materials provide background for the foregoingdescription, and the entire disclosure of each of the followingpublications is incorporated herein by reference.

-   D. A. Nowak, C. Grefkes, M. Dafotakis, J. Kust, H. Karbe, and G. R.    Fink. Dexterity is impaired at both hands following unilateral    subcortical middle cerebral artery stroke. European Journal of    Neuroscience. 2007; 25(10):3173-3184.-   G. Kwakkel and B. Kollen, Predicting improvement in the upper    paretic limb after stroke. Restorative Neurology and Neuroscience.    2007; 25(5):453-460.-   B. Steenbergen, J. Charles, and A.M. Gordon, Fingertip force control    during bimanual object lifting in hemiplegic cerebral palsy.    Experimental Brain Research. 2008; 186(2):191-201.-   J. M. Blennerhassett, L. M. Carey, and T. A. Matyas, Clinical    measures of handgrip limitation relate to impaired pinch grip force    control after stroke. Journal of Hand Therapy. 2008; 21(3):245-253.-   N. Byl, et al Effectiveness of Sensory and Motor Rehabilitation of    the Upper Limb Following the Principles of Neuroplasticity: Patients    Stable Poststroke. Neurorehab and Neural Repair. 2003; 17:176-191.-   Y. Tian, L. G. Kang, H. Y. Wang, and Z. Y. Liu, Biofeedback therapy    improves motor function following stroke. Neural Regeneration    Research. 2010; 5(7):538-544.-   O. Armagan, Tascioglu F., Oner C. Electromyographic biofeedback in    the treatment of the hemiplegic hand: a placebo-controlled study. Am    J Phys Med Rehabil. 2003; 82:856-61.-   K. S. Turker. Electromyography: Some Methodological Problems and    Issues. Physical Therapy. 1993; 73(10), 698-710.-   M. T. Wininger, N. H. Kim, W. Craelius. Pressure Signature of    Forearm as Predictor of Grip Force. J Rehab Res Dev. 2008;    4(6):883-892.-   S. Phillips and W. Craelius. Residual Kinetic Imaging: A Versatile    Interface for Prosthetic Control. Robotica. 2005; 23: 277-82.-   K. Grice, K. A. Vogel, L. Viet, A. Mitchell, S. Muniz, M. A.    Vollmer. Adult norms for a commercially available Nine Hole Peg Test    for finger dexterity. Am J Occ Ther. 2003; 57:570-3.-   P. Langhorne, R. Wagenaar, and C. Partridge. Physiotherapy after    stroke: more is better? Physiotherapy Research International. 1996;    1(2):75-88.-   S. Hesse, et al. Ankle Muscle Activity Before and After Botulinum    Toxin Therapy for Lower Limb Extensor Spasticity in Chronic    Hemiparetic Patients. Stroke. vol. 27, pp. 455-460, 1996.-   L. F. Teixeira-Salmela, S. J. Olney, S. Nadeau, and B. Brouwer.    Muscle Strengthening and Physical Conditioning to Reduce Impairment    and Disability in Chronic Stroke Survivors. Arch Phys Med Rehabil.    1999; 80:1211-1218.-   B. T. Volpe, et al. A novel approach to stroke rehabilitation:    Robot-aided sensorimotor stimulation. Neurology. 2000;    54(10):1938-1944.-   A. Prochazka, D. Gillard, and D. J. Bennett. Positive Force Feedback    Control of Muscles. J Neurophys. 1997; 77(6):3226-36.-   G. Alon, A. F. Levitt, P. A. McCarthy. Functional Electrical    Stimulation Enhancement of Upper Extremity Functional Recovery    During Stroke Rehabilitation: A Pilot Study. Neurorehabilitation and    Neural Repair. 2007; 21(3):207-15.-   R. K. Bode and A. W. Heinemann. Course of functional improvement    after stroke, spinal cord injury, and traumatic brain injury. Arch    Phys Med and Rehab. 2002; 83(1):100-106.-   S. E. Fasoli, H. I. Krebs, and N. Hogan. Robotic Technology and    Stroke Rehabilitation: Translating Research into Practice. Topics in    Stroke Rehab. 2004; 11(4):11-19.

It will be recognized by those skilled in the art that changes ormodifications may be made without departing from the broad inventiveconcepts of the invention. It should therefore be understood that thisinvention is not limited to the particular embodiments described herein,but is intended to include all changes and modifications that are withinthe scope and spirit of the invention as set forth in the claims.

1. A system for providing therapeutic biofeedback, comprising: a sensingdevice for monitoring a characteristic of a patient, and providingoutput signals indicative of the monitored characteristic; a processoroperable to receive the signals from the sensing device, wherein theprocessor can be programmed with predetermined values representative ofa desired therapeutic activity, and wherein the processor is operable tocompare the signals received from the sensing device with thepredetermined values to provide feedback to the patient; a feedbackelement connected with the processor, wherein the feedback elementreceives signals from the processor and provides a human recognizablefeedback based on the signals from the processor.
 2. The system of claim1 wherein the sensing device comprises a plurality of force detectorsfor detecting surface movement applied to the detectors by the patientin response to movement by the patient.
 3. The system of claim 1 whereinthe sensing device comprises a plurality of spaced apart sensors.
 4. Thesystem of claim 1 wherein the sensing device comprises a force sensingresistor.
 5. The system of claim 1 wherein the sensing device comprisesa connector readily connectable to the patient to maintain the sensingdevice in an operable proximity to the patient.
 6. The system of claim 1wherein the sensing device comprises a plurality of sensors and theprocessor comprises a set-up mode in which the patient performs thedesired therapeutic activity and the processor creates a template ofsensor values indicative of the desired therapeutic activity, andwherein the processor comprises a therapy mode during which theprocessor compares the signals received from the sensing device with thetemplate determined during the set-up mode, wherein the processorprovides signals to the feedback element based on a comparison of thesignals from the sensing device and the template.
 7. The system of claim1 wherein the feedback element provides at least one of: a visualsignal, an audial signal and a tactile signal.
 8. The system of claim 1wherein the feedback element comprises a display for providing visualfeedback based on the signals from the processor.
 9. The system of claim1 wherein the system comprises an output element for providing a humanlyperceivable cue for commencing the desired therapeutic activity.
 10. Thesystem of claim 9 wherein the feedback element comprises an audioelement for providing a audial signal to the patient.
 11. A system forproviding therapeutic biofeedback, comprising: a sensor for detectingmuscular activity and providing output signals indicative of thedetected muscular activity; a processor operable to receive the signalsfrom the sensor, wherein the processor includes a set up mode forprogramming the processor with values representative of a desiredtherapeutic activity, and wherein the processor is operable to comparethe signals received from the sensor with the predetermined values toprovide feedback to the patient; and a feedback device connected withthe processor, wherein the feedback device receives signals from theprocessor to provide human recognizable feedback.
 12. The system ofclaim 11 wherein the sensor comprises a plurality of force detectors fordetecting surface movement applied to the sensor by the patient inresponse to movement by the patient.
 13. The system of claim 11 whereinthe sensing device comprises a force sensing resistor.
 14. The system ofclaim 11 wherein the sensor is one of a plurality of spaced apartsensors, wherein in the set-up mode the processor is operable to receivesignals from the sensors when the patient performs the desiredtherapeutic activity and calculate the predetermined values in responseto the signals received during the set-up mode.
 15. The system of claim14 wherein the processor comprises a therapy mode during which theprocessor compares the signals received from the sensor with thepredetermined values calculated during the set-up mode, wherein theprocessor provides signals to the feedback element based on a comparisonof the signals from the sensors and the predetermined values.
 16. Thesystem of claim 1 wherein the feedback element provides at least one of:a visual signal, an audial signal and a tactile signal.
 17. The systemof claim 1 wherein the feedback element comprises a display forproviding visual feedback based on the signals from the processor. 18.The system of claim 1 wherein the system comprises an output element forproviding a humanly perceivable cue for commencing the desiredtherapeutic activity.
 19. The system of claim 9 wherein the feedbackelement comprises an audio element for providing a audial signal to thepatient.
 20. A method for providing therapeutic biofeedback, comprisingthe steps of: sensing a characteristic indicative of muscular activityof a patient; providing a signal corresponding to the sensedcharacteristic; comparing the signal with predetermined valuesindicative of a desired therapeutic activity; and providing humanrecognizable feedback to the patient in response to the step ofcomparing the signal.
 21. The method of claim 20 wherein the step ofsensing comprises the step of detecting surface movement applied to asensor by the patient in response to movement by the patient.
 22. Themethod of claim 21 wherein the sensor device comprises a force sensingsensor and the step of providing a signal comprises providing a signalfrom the force sensing sensor.
 23. The method of claim 21 wherein in aset-up mode a processor is operable to receive signals from a sensorwhen the patient performs a desired therapeutic activity and wherein themethod comprises the step of calculating the predetermined values inresponse to the signals received during the set-up mode.
 24. The methodof claim 23 comprising the step of operating the processor in a therapymode during during which the processor compares the signals receivedfrom the sensor with the predetermined values calculated during theset-up mode, wherein the processor provides signals to the feedbackelement based on a comparison of the signals from the sensor and thepredetermined values.